Some Android Apps are Libre Software Licensed, has fully free and modifiable source code. Here is How to on Building Custom Android App From Open Source Android Apps.

Building Custom Android App From Open Source Android Apps

If you are an indie developer, you have to do the hard work of manually testing all by yourself. Before releasing your app to Play Store, make release to a controlled group of users as alpha version. On Reddit there are subreddits where you can find beta testers.

F-Droid has huge number of applications :

Vim

1

https://f-droid.org/en/

There is FoSSDroid :

Vim

1

https://fossdroid.com/

GitHub will have some such with android and android-application tag :

Vim

1

https://github.com/topics/android-application

Advertisement

---

Coding Part of Building Custom Android App From Open Source Android Apps

One essentially needs to find out an existing application which is closer to the own need. Then you can import/open that source code in any Android development

As example to help your thought, if we create a native Android application for our this website, to use the application we may want to use Facebook or Twitter account to login or create separate login for the application. We may use a different server to work as mobile app backend to increase security and offer reading, features in different way than desktop application does. In that case, we may need to study a smaller application for Facebook or Twitter account to login function. Here is a good blog post for more graded source codes :